Preparation of carboxylic acids by the reduction of beta lactones



Patented Oct. 11, 1949 PREPARATION OF CARBOXYLIC ACIDS BY THE REDUCTION OF BETA; LACTONES John R. Caldwell, Kingsport, Tenn., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application May 15, 1946, Serial No. 670,037

8 Claims. 1

This invention relates to the preparation of aliphatic acids and more particularly to the preparation of straight chain and branched chain substituted aliphatic carboxylic acids by the catalytic hydrogenation of beta hydroxy carboxylic acid lactones. The invention provides a new and valuable method for the preparation of the lower aliphatic carboxylic acids as represented by propionic acid, butyric acid, betamethyl butyric acid, beta-methyl valeric acid, beta-ethyl valeric acid, hexanoic acid and other such acids discussed herein.

The invention is of particular value because a large variety of substituted beta-lactones are readily available from the condensation of ketene with aldehydes and ketones. Thus the invention provides a convenient and economical method for the preparation of many straight and branched chain aliphatic carboxylic acids which heretofore could be prepared only with difiiculty' by using involved and expensive syntheses.

An object of the invention is to provide a method for the preparation of saturated aliphatic acids having the general structure R-CH-CHFGO OH wherein R and R represent alkyl radicals containing 1 to 4 carbon atoms, or hydrogen.

Another object of the invention is to provide a process for converting beta hydroxy carboxylic acid lactones to substituted aliphatic acids of the above described chemical structures and constitution. The beta hydroxy carboxylic acid lactones, otherwise known as beta lactones, employed in the process have the general structure wherein R and R have the significance described in the above paragraph.

In accordance with the invention these and other objects are attained by the catalytic hydrogenation of beta-lactones while employing elevated temperatures and pressures under carefully controlled conditions. Considered from a broad aspect, the invention comprehends converting a beta lactone group to a carboxyl group as shown in the following equation:

beta lactone carboxylic acid Hydrogenation may be carried out in any standard apparatus usually employed for this purpose. It has been found that a Raney nickel catalyst works exceedingly well in this reaction.

The cleavage of a beta lactone by hydrogenolysis to give a free carboxylic acid is a very unusual and unexpected reaction. structurally, beta lactones are cyclic esters formed by the esterification of a hydroxyl group with a carboxyl group. According to the literature on the reduction or hydrogenolysis of gamma lactones, the cleavage would be expected to occur between the oxygen atoms to give a 1,3-glycol according to the equation: I

This is indicated in Reactions of Hydrogen, page 78, by Adkins, University of Wisconsin Press, 1937, where the statement is made that gamma lactones are converted to glycols in yields. It would, therefore, be expected that beta lactones would follow a similar reaction and yield 1,3 glycols upon hydrogenation. However, I have found that the reaction takes an entirely different and unexpected course, and when carried out under appropriate conditions saturated aliphatic carboxylic acids are formed in good yields, while glycols are produced in minor quantities or not at all.

The various beta hydroxy carboxylic acid lactones employed as the starting materials may be prepared by condensing ketene or its aliphatic homologs with a carbonyl compound such as an aldehyde or a ketone of the type and by the methods described in U. S. Patent 2,356,459 of August 22, 1944. For example, gaseous ketene is passed into the carbonyl compound also in a vapor form and reacted at a temperature below 25 C. in the presence of a Friedel-Crafts catalyst such as BF3, A1013, Zn-Clz or others known in the art to form beta lactone. By thus employing different carbonyl and aldehyde compounds the lactone structure can correspondingly be varied.

The present invention by which such lactones are hydrogenated into valuable fatty acids is further illustrated in the following examples:

Example I .Hydrogenation of beta-hydroxy propz'om'c acid lactone to propionic dcid Formaldehyde and ketene are condensed in approximately equimolecular proportions in the presence of a boron fluoride catalyst, after the method described in Example I of U. S. Patent 2,356,459, to produce a substantial yield of the 3 lactone of p-hydroxy propionic acid. 100 grams of this lactone is placed in a rocking autoclave and 2 grams of Fancy nickel catalyst washed with 1 4 dioxane are added. Air is flushed out of the autoclave by a stream of hydrogen and the autoclave is set in motion and then subjected to a hydrogen pressure of 1500 pounds per square inch while the temperature is raised to 125-140 C. As the hydrogen pressure in the autoclave drops, owing to hydrogenation, additional hydrogen is admitted to restore the initial pressure, and this procedure is repeated until no more hydrogen is used in the hydrogenolysis. The reaction is completed in from 1 to 2 hours and may be shown as follows:

i HO-CH2 H: HCH.CHz-COOH I Raney I G=O nickel H fi-lactone Propionic acid The autoclave is allowed to cool and the reaction mixture is decanted from the catalyst. The product may be filtered to remove the remaining catalyst and is then distilled at reduced pressure to give a propionic acid of high purity.

Example II.-Hydrogenation of beta-hydromy batyric acid lactone to butyric acid Acetaldehyde and ketene are condensed in the presence of a boron fluoride catalyst after the method described in Example 3 of U. S. Patent 2,356,459 to yield purified beta-hydroxy butyric acid lactone. 100 grams of this beta-hydroxy butyric acid lactone is placed in a suitable autoclave and hydrogenated in the presence of 2 grams of Raney nickel which has been washed with 1-4 dioxane. Hydrogen under a pressure of 1500 pounds per square inch is employed with a temperature of 150-160 C. Reduction is complete in 1 to 2 hours. The reaction is shown in the following equation:

The product is filtered to remove the catalyst and is distilled to give 80-90 grams of butyric acid, B. P. 163 0. Equivalent weight 88. Theoretical equivalent weight 88.

Example III.-Hyclrogenat2'0n of beta-hydrowy-3- methyl butyric lactone to beta-methyl butyrz'c acid Acetone and ketene are reacted at about 30 C. with boron fluoride as the catalyst to give beta-S-methyl butyric lactone. The reaction was conducted a manner similar to that disclosed in Example 3 of U. S. Patent 2,356,459. This lactone is reduced in an autoclave with Raney nickel at a temperature of 130-150 C. using 1500 pounds per square inch of hydrogen. The reaction is shown by the following equation:

The yield is 9095% beta-3-methyl butyric acid, boiling at 175 C./1'7'l mm. Equivalent weight 102. Theoretical equivalent weight 102.

Example IV.-Hydrgenation of beta-hydromy-3- methyl oalerz'c lactone to beta-methyl valeric acid Ketene is condensed with methyl ethyl ketone 4 at about 25 C. with boron fluoride as the catalyst to give the lactone beta-hydroxy-3-methyl valeric acid lactone.

300 grams of this lactone were placed in a rocking autoclave with 5 grams Raney nickel which had been washed with dioxane. Hydrogen is introduced and the temperature is raised to 100-120 C. Reduction is complete in 1 to 3 hours. The reaction may be shown as follows:

CHa onward-( 1H, H, CHaCHzCHCHgCOOH o=o nickel CH3 A yield of 280-300 grams beta-methyl valeric acid is obtained boiling at 195 C. Equivalent weight 117. Theoretical equivalent weight 116.

Example V.-Hydrogenation of the lactone of beta-4-methyl valeric acid to gamma-methyl valerz'c acid Raney CH3 OC=O nickel CH3 The product is filtered to remove catalyst and is then distilled to give -90 grams of acid.

Example VI Ketene and butyraldehyde are condensed in the presence of a boron fluoride catalyst after the method described in U. S. Patent 2,356,459 to give the lactone of beta hexanoic acid. grams of this beta lactone was reduced in an autoclave in the presence of 5 grams of Raney nickel. Hydrogen was admitted under a pressure of 1500 pounds per square inch. The temperature of the reaction was kept within to C. The reaction was as follows:

+112 CHa(CHz)4COOH Raney nickel The product was filtered and when distilled gave 85-90 grams of hexanoic acid.

These examples illustrate preferred conditions for making the lower fatty acids from the beta lactones of such acids. It will be understood that a relatively large number of such acids can be produced in a like manner by employing the great variety of beta lactones disclosed in U. S. Patent 2,356,459. Hydrogenation of the beta-lactones is carried out preferably in the usual type of rocking or stirring heated autoclaves. Pressures of 500-1500 pounds of hydrogen may be employed. The reaction may be conducted at a temperature range of approximately 100-200 C. but actually most of the lactones can be reduced at 130-150 C. R'aney nickel is a satisfactory catalyst but other types of highly active metallic catalysts may be used, such as copper chromite, nickel on kieselguhr and the like. The Raney nickel catalyst is prepared as shown in U. S. Patents 1,628,190 and 1,915,473 by a method of leaching aluminum out of a nickel-aluminum alloy with sodium hydroxide.

I claim:

1. The process for preparing aliphatic saturated carboxylic acids from the beta lactones of the acids to be prepared which comprises hydrogenating in a closed vessel, in the presence of a metallic hydrogenation catalyst, at a temperature above 100 C. a beta lactone having the general structure:

RI R( CH2 wherein R and R. each represents a member selected from the class consisting of hydrogen and an alkyl group containing 1 to 4 carbon atoms.

2. The process for preparing aliphatic saturated carboxylic acids from beta lactones which comprises hydrogenating, in a closed vessel at super atmospheric pressures and in the presence of a metallic hydrogenation catalyst at a temperature within the range of 100 C. to 200 C., a compound having the general structure:

RI R-CH2 wherein R and R each represents a member selected from the class consisting of hydrogen and an alkyl group containing 1 to 4 carbon atoms.

The process for preparing propionic acid. which comprises hydrogenating in a closed vessel at super atmospheric pressures and in the presence of a metallic hydrogenation catalyst at a temperature of approximately 140 C. the lactone of beta-hydroxy propionic acid.

4. The process for preparing butyric acid which comprises hydrogenating in a closed vessel at super atmospheric pressures and in the presence of a metallic hydrogenation catalyst at a temperature within the range of approximately 150-160 C., the beta-hydroxy lactone of butyric acid.

5. The process for preparing beta-methyl valeric acid which comprises hydrogenating in a closed vessel at super atmospheric pressures and in the presence of a metallic hydrogenation catalyst at a temperature of approximately 140 C. the lactone of beta-hydroxy-3-methyl valeric acid.

mately 150 C., the lactone of beta-hydroxy butyric acid.

8. The process for preparing beta-methyl valeric acid which comprises hydrogenating in a closed vessel at 1500 poundsper square inch of hydrogen and in the presence of a nickel hydrogenation catalyst of the Raney type at a temperature of approximately C., the lactone of betahydroxy-S-methyl valeric acid.

JOHN R. CALDWELL.

REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PA'IIElNTS Number Name Date 2,037,876 Bousquet Apr. 21, 1936 2,361,036 Kung Oct. 24, 1944 OTHER REFERENCES Kiliani et al., Ber. Deut. Chem, Vol. 17 p. 1301 Kiliani et al., Ber. Deut. Chem., vol. 18, p. 643 (1885).

Wessely et al., Monatsh. fur Chem., vol. 71, pp. 27-29 (1937).

Allen et al., J. Am. Chem. Soc., vol. 61, pp. 843-846 (1939).

Boese, Ind. 8a En. Chem., v01. 32, page 20 (1940).

Benneville et al., J. Am. Chem. Soc., vol. 62, pp.

Benneville et al., J. Am. Chem. Soc., vol. 62, pp. 3067-3070 (1940).

Johansson, Beilstein Suppl.) vol. 17, p. 130.

(Handbuch, 4th ed., 

